Laminating adhesives based on primary hydroxyl-containing curatives

ABSTRACT

A curative containing two or more primary hydroxyl groups per molecule and one or more moieties derived from a secondary hydroxyl-containing polyol such as polypropylene glycol is prepared in a multistage process wherein the secondary hydroxyl-containing polyol is end-capped with an excess of a reactant such as a polybasic acid and the resulting functionalized intermediate is then reacted with a polyol such as glycerin or diethylene glycol containing primary hydroxyl groups. Such curatives may be used in combination with isocyanate-functionalized polyurethane prepolymers to provide two component adhesives useful for laminating thin films and/or foils.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.15/442,955 filed on Feb. 27, 2017 which is a continuation of U.S. patentapplication Ser. No. 12/765,290 filed on Apr. 22, 2010, now abandoned,which is a continuation of U.S. patent application Ser. No. 11/065,501filed on Feb. 24, 2005, now abandoned, which is a continuation-in-partof U.S. patent application Ser. No. 10/986,591 filed on Nov. 12, 2004,which was granted on Jan. 13, 2015 as U.S. Pat. No. 8,933,188, thecontents of each of which is incorporated herein by reference in itsentirety.

FIELD OF THE INVENTION

The present invention provides two component laminating adhesives basedon polyurethanes in which one of the components contains a curativebearing primary hydroxyl groups and the other component contains anisocyanate-functionalized compound. The curative is prepared by amultistep process comprising reacting a first polyol containingpredominately secondary hydroxyl groups with a stoichiometric excess ofa reactant selected from the group consisting of polybasic acids,polybasic acid anhydrides, polybasic acid esters, and polyisocyanates toform an intermediate containing at least about two terminal functionalgroups per molecule selected from the group consisting of isocyanate,carboxylic acid and carboxylic acid ester and reacting said intermediatewith a stoichiometric excess of a second polyol containing predominatelyprimary hydroxyl groups. The resulting curative thus typically containsat least four ester or urethane linkages per molecule. The twocomponents are combined and the resulting adhesive used to laminate athin polymeric film or foil to one or more thin polymeric films orfoils.

BACKGROUND OF THE INVENTION

Laminating adhesives are widely used in the manufacture of film/foillaminates. Among many such known systems, the use of polyurethane basedlaminating adhesives is preferred because of their many desirableproperties including good adhesion, peel strength, heat seal strengthand resistance to aggressive filling goods. Typically, anisocyanate-containing polyurethane prepolymer obtained by the reactionof excess diisocyanate with a polyether and/or polyester containing twoor more active hydrogen groups per molecule is used in combination witha second component. The second component usually is a polyether and/orpolyester functionalized with two or more hydroxyl groups or the likeper molecule. The two components are combined in a predetermined ratioand applied on one of the film or foil substrates, which is thenlaminated to the second substrate. Application may be from a solution ina suitable solvent using gravure or smooth roll coating cylinders orfrom a solvent-free state using special application machinery.

The second component is commonly comprised of hydroxyl-terminatedpolyesters prepared by reacting polybasic acids or anhydrides with astoichiometric excess of a mixture of glycols that have primary orsecondary hydroxyl groups and/or glycols that contain both primary andsecondary hydroxyl groups in the same molecule (such as glycerol). Manysecondary hydroxyl-containing polyols can be used to advantage to makepolyester polyols. In particular, commercially available polypropyleneglycols such as dipropylene glycol, tripropylene glycol, PPG 425, PPG1025, PPG 2025 and PPG 3025 all have terminal hydroxyl groups which arepredominately (e.g., at least 90%) secondary. It will often be desirableto prepare polyester polyols incorporating higher molecular weightpolypropylene glycols, as such substances tend to improve theflexibility and viscosity properties of polyester polyols.

Due to the faster reaction rates of primary hydroxyl groups withcarboxylic acid groups or acid anhydrides, if the glycol component to bereacted with the polybasic acid component contains both primary andsecondary hydroxyl groups, the predominate esters formed are with theprimary hydroxyl groups. The secondary hydroxyl groups remainpredominately unreacted. As the polymerization/condensation proceeds, apolyester polyol having a higher molecular weight than desired isgenerated as a result of the preferential reaction of the glycolscontaining primary hydroxyl groups. A high proportion of the glycolscontaining secondary hydroxyl groups remain unreacted, however. Theresulting reaction product thus can be a mixture of a relatively highmolecular weight polyester polyol and unreacted secondaryhydroxyl-containing glycol, which may not provide favorable performancewhen used as a curative in a two component laminating adhesive.

If the secondary hydroxyl groups do eventually react, the polyester willstatistically tend to be terminated with secondary hydroxyl groups. Thisis a disadvantage, since termination of the polyester with primaryhydroxyl groups is often desired so that reaction withisocyanate-functionalized prepolymers will occur at a relatively fastrate, leading to quick curing of the adhesive. A polyester polyol thathas secondary hydroxyl groups will react much more slowly withisocyanate-functionalized prepolymers.

SUMMARY OF THE INVENTION

The present invention provides a two component laminating adhesivecomprising Component A and Component B, wherein Component A comprises atleast one isocyanate-functionalized compound and Component B comprises acurative containing at least about two primary hydroxyl groups permolecule. The curative is obtained by a process comprising reacting afirst polyol containing predominately secondary hydroxyl groups with astoichiometric excess of a reactant selected from the group consistingof polybasic acids, polybasic acid anhydrides, polybasic acid esters,and polyisocyanates to form an intermediate containing at least abouttwo terminal functional groups per molecule selected from the groupconsisting of isocyanate, carboxylic acid and carboxylic acid ester. Theintermediate is reacted with a stoichiometric excess of a second polyolcontaining predominately primary hydroxyl groups to form the curative.

A laminate may be formed by combining the two components to provide anadhesive and then using the adhesive to adhere one polymeric film ormetallic foil to another polymeric film or metallic foil. The adhesivelayer between the film or foil layers of the laminate is then cured.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS OF THE INVENTION

The curative utilized as a constituent of the laminating adhesive of thepresent invention is obtained by a multistage process. In one step, afirst polyol containing predominately secondary hydroxyl groups isreacted with a stoichiometric excess of a reactant selected from thegroup consisting of polybasic acids, polybasic acid anhydrides,polybasic acid esters, and polyisocyanates to form an intermediatecontaining at least about two terminal functional groups per moleculeselected from the group consisting of isocyanate, carboxylic acid andcarboxylic acid ester.

In the context of this invention, the term “predominately” means “morethan half” (i.e., “more than 50%”). Thus, the first polyol is a compoundor mixture of compounds containing at least about two hydroxyl groupsper molecule wherein more than half the hydroxyl groups are secondaryhydroxyl groups. In one embodiment, more than about 75% of the hydroxylgroups are secondary. In another embodiment, more than about 90% of thehydroxyl groups are secondary. Glycol oligomers and polymers are used asthe first polyol in one embodiment of the present invention. Forexample, the first polyol may be an oligomer or polymer of 1,2-propyleneglycol. Illustrative oligomers of 1,2-propylene glycol includedipropylene glycol, tripropylene glycol, tetrapropylene glycol and thelike. Illustrative polymers of 1,2-propylene glycol include the polymersobtainable by reacting a polyhydroxyl-functionalized initiator such aswater, 1,2-propylene glycol, 1,4-butanediol, glycerol,trimethylolpropane or the like with propylene oxide in the presence of acatalyst such as an alkali metal or a double metal cyanide complexcatalyst. Polypropylene glycols having number average molecular weightsof from about 200 to about 10,000 or about 300 to about 5000 aresuitable for use as the first polyol in the present invention, forexample. Other polyoxyalkylene glycols having predominately secondaryhydroxyl groups may also be utilized.

The reactant which is reacted in stoichiometric excess with the firstpolyol may be one or more substances selected from among polybasicacids, polybasic acid anhydrides, polybasic acid esters, andpolyisocyanates.

Suitable polybasic acids include substances containing at least abouttwo carboxylic acid groups per molecule. The polybasic acids may bealiphatic, cycloaliphatic, aromatic and/or heterocyclic. They may whereappropriate be substituted, by alkyl groups, alkenyl groups, ethergroups or halogens, for example. Examples of suitable polybasic acidsinclude succinic acid, adipic acid, suberic acid, azelaic acid, sebacicacid, phthalic acid, isophthalic acid, terephthalic acid, trimelliticacid, maleic acid, fumaric acid, dimer fatty acid (i.e., dimerizedunsaturated fatty acids) or trimer fatty acid or mixtures of two or morethereof. In one embodiment of the invention, the polybasic acid is alinear aliphatic dicarboxylic acid containing from 4 to 12 carbon atomsper molecule or a mixture of such dicarboxylic acids. The polybasic acidmay, for example, have a structure corresponding to the general formulaHOC(═O)—(CH₂)_(n)—C(═O)OH, where n is an integer of from 2 to 10.

Suitable polybasic acid anhydrides include the anhydrides of thepolybasic acids mentioned or described hereinabove. The anhydride oforthophthalic acid is an example of a polybasic acid anhydride that canbe used in the present invention.

Suitable polybasic acid esters include the esters of the polybasic acidsmentioned or described hereinabove, particularly the lower alkyl (e.g.,C₁-C₃) esters of such polybasic acids.

Suitable polyisocyanates include organic compounds containing two ormore isocyanate (NCO) functional groups per molecule. These includecompounds of the general structure O═C═N—X—N═C═O, where X is analiphatic, alicyclic or aromatic radical, such as an aliphatic oralicyclic radical having from 4 to 18 carbon atoms. Illustrativepolyisocyanates include, for example, 1,5-naphthylene diisocyanate,4,4′-diphenylmethane diisocyanate (MDI), hydrogenated MDI (H₁₂MDI),xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI),4,4′-diphenyldimethyl-methane diisocyanate, di- andtetraalkylenediphenylmethane diisocyanate, 4,4′-dibenzyl diisocyanate,1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, the isomers oftolylene diisocyanate (TDI), 1-methyl-2,4-diisocyanatocyclohexane,1,6-diisocyanato-2,2,4-trimethylhexane,1,6-diisocyanato-2,4,4-trimethylhexane,1-isocyanatomethyl-3-isocyanato-1,5,5-trimethylcyclohexane (IPDI),chlorinated and brominated diisocyanates, phosphorus-containingdiisocyanates, 4,4′-diisocyanatophenylperfluoroethane,tetramethoxybutane 1,4-diisocyanate, butane 1,4-diisocyanate, hexane1,6-diisocyanate (HDI), dicyclohexylmethane diisocyanate, cyclohexane1,4-diisocyanate, ethylene diisocyanate, bisisocyanatoethyl phthalateand also diisocyanates having reactive halogen atoms, such as1-chloromethyiphenyl 2,4-diisocyanate, 1-bromomethylphenyl2,6-diisocyanate, and 3,3-bischloromethyl ether 4,4′-diphenyldiisocyanate.

Sulfur-containing polyisocyanates are obtained, for example, by reacting2 mol of hexamethylene diisocyanate with 1 mol of thiodiglycol ordihydroxydihexyl sulfide. Further diisocyanates which can be used are,for example, trimethylhexamethylene diisocyanate,1,4-diisocyanatobutane, 1,12-diisocyanatododecane and dimer fatty aciddiisocyanate. Particularly suitable are the following: tetramethylene,hexamethylene, undecane, dodecamethylene, 2,2,4-trimethylhexane,1,3-cyclohexane, 1,4-cyclohexane, 1,3- or 1,4-tetramethylxylene,isophorone, 4,4-dicyclohexylmethane and lysine ester diisocyanates. Inone embodiment of the invention, tetramethylxylylene diisocyanate(TMXDI) is utilized as the polyisocyanate.

Examples of suitable polyisocyanates having a functionality of at leastthree are the trimerization and oligomerization products of thepolyisocyanates already mentioned above, such as are obtainable, withthe formation of isocyanurate rings, by appropriate reaction ofpolyisocyanates, preferably of diisocyanates. Where oligomerizationproducts are used, those particularly suitable have a degree ofoligomerization of on average from about 3 to about 5.

Isocyanates suitable for the preparation of trimers are thediisocyanates already mentioned above, particular preference being givento the trimerization products of the isocyanates HDI, MDI or IPDI.

Likewise suitable for use as the polyisocyanate are the polymericisocyanates, such as are obtained, for example, as a residue in thedistillation bottoms from the distillation of diisocyanates. PolymericMDI (PMDI), which may be obtained from the distillation residue duringthe distillation of MDI, is particularly suitable.

The first polyol(s) and reactant(s) are reacted for a time and at atemperature effective to convert most or preferably essentially all ofthe hydroxyl groups on the first polyol to either urethane or estergroups (depending upon the type of reactant selected for use). Theamounts of the first polyol(s) and the reactant(s) which are reacted areadjusted such that the reactant is in stoichiometric excess relative tothe first polyol. Preferably, the molar ratio of R/OH (where Rrepresents the functional groups on the reactant capable of reactingwith the hydroxyl groups of the first polyol, e.g., —CO₂H, —CO₂R′ whereR′═C₁-C₃ alkyl, or —NCO) is at least about 2. Conditions effective toachieve such conversion of the first polyol hydroxyl groups will beapparent to those skilled in the art and will vary somewhat dependingupon the reactant and first polyol selected.

For example, where the reactant is a polybasic acid or polybasic acidester such that the first polyol hydroxyl groups must undergoesterification, reaction temperatures of from about 100 degrees C. toabout 300 degrees C. and reaction times of from about 1 to about 12hours are typically suitable. The esterification may, if desired, beaccelerated (increased in rate) and/or performed at a lower temperatureby carrying out the reaction in the presence of a catalyst, includingany of the conventional esterification catalysts known in the art suchas, for example, acids (e.g., sulfuric acid, phosphoric acid, sulfonicacids), bases (e.g., alkali metal and alkaline earth metal oxides andhydroxides such as potassium hydroxide, lithium hydroxide), organotincompounds (e.g., dibutyl tin dilaurate), and titanium compounds (e.g.,titanium tetraisopropoxide, titanium tetrabutoxide). Typically, thecatalyst is present at a concentration of from about 0.001 to about 0.1percent by weight of the combined weight of fatty acid triglyceride(s)and polyalcohol(s). Following esterification, the catalyst may beremoved from the polyhydroxyl-functionalized transesterificationproduct. The esterification may be carried out under vacuum tofacilitate the removal of water, alcohol or other volatiles that mayform.

Where the reactant is a polyisocyanate, somewhat milder reactionconditions (e.g., about 20 degrees C. to about 100 degrees C.) willtypically suffice to convert the first polyol hydroxyl groups tourethane groups due to the relatively high reactivity of the isocyanategroups of the polyisocyanate. However, if desired, the reaction may beaccelerated by the use of any of the substances known in the art to beeffective in catalyzing urethane formation, such as tin compounds,tertiary amines and the like.

The intermediate formed as a result of the aforedescribed reaction ofthe first polyol and the reactant contains at least about two terminalfunctional groups per molecule selected from the group consisting ofisocyanate, carboxylic acid and carboxylic acid ester. This intermediateis subsequently reacted with a stoichiometric excess of a second polyolcontaining predominately primary hydroxyl groups.

The second polyol may be a compound or mixture of compounds containingat least about two hydroxyl groups per molecule wherein more than halfthe hydroxyl groups are primary hydroxyl groups. In one embodiment, morethan about 60% of the hydroxyl groups are primary. In anotherembodiment, essentially all of the hydroxyl groups of the second polyolare primary. Aliphatic compounds containing from two to ten carbonatoms, from two to five hydroxyl groups, from two to five primaryhydroxyl groups, and 0 to two secondary hydroxyl groups (with the ratioof primary:secondary hydroxyl groups being preferably at least 2:1) areamong the compounds suitable for use as the second polyol. Glycolscontaining two or more primary hydroxyl groups per molecule may be usedas the second polyol, for example. Examples of such glycols includeglycerol, ethylene glycol, 1,3-propylene glycol, 1,4-butanediol,1,6-hexanediol, neopentyl glycol, 2-methyl-1,3-propanediol,pentaerythritol, trimethylolpropane, trimethylolethane,1,2,6-hexanetriol, ethoxylates of polyalcohols (such as any of theaforementioned glycols as well as compounds containing two or moresecondary hydroxyl groups), and the like. Oligomers and polymers of suchglycols are used as the second polyol in one embodiment of the presentinvention. For example, the second polyol may be an oligomer or polymerof ethylene glycol. Illustrative oligomers of ethylene glycol includediethylene glycol, triethylene glycol, tetraethylene glycol and thelike. Mixtures of different compounds may be used as the second polyolif so desired.

The second polyol reacted with the intermediate for a time and at atemperature effective to convert most or preferably essentially all ofthe terminal functional groups on the intermediate to either urethane orester groups (depending upon the type of terminal functional grouppresent in the intermediate). Generally speaking, such conditions willtypically be similar to those described hereinabove in connection withthe preparation of the intermediate. The amounts of the second polyol(s)and the intermediate which are reacted are adjusted such that the secondpolyol is in stoichiometric excess relative to the intermediate.Preferably, the molar ratio of R/OH (where R is the terminal functionalgroup (e.g., —CO₂H, —CO₂R′ where R′═C₁-C₃ alkyl, or —NCO) on theintermediate capable of reacting with the hydroxyl groups of the secondpolyol) is at least about 2.

Typically, the curative thereby produced by reacting the intermediatewith the second polyol will have an equivalent weight per hydroxyl groupof from about 300 to about 1000. The viscosity of the curative istypically from about 1000 to about 10,000 cps at 25 degrees C.

In one embodiment of the invention, the curative produced has thestructure:Y—O—C(═O)—Z—C(═O)—O—CH(CH₃)—CH₂—O—(C₃H₆O)_(n)—CH₂—CH(CH₃)—O—C(═O)—Z′—C(═O)—O—Y′

wherein Y and Y′ are the same or different and are selected from thegroup consisting of HO—CH₂—CH(OH)—CH₂— and HO—(CH₂—CH₂—O—)_(p)—CH₂—CH₂—,Z and Z′ are the same or different and are selected from the groupconsisting of —C₆H₄— (i.e., a divalent benzene radical) and —(CH₂)_(o)—,p is 0 or an integer of 1 to 3, o is an integer of from 2 to 10, and nis 0 or an integer of from 1 to 100.

The curative prepared as described hereinabove may be utilized as aconstituent of Component B of the two component laminating adhesive ofthe present invention. For example, from about 1 up to 100 weightpercent of Component B may be comprised of one or more such curatives.Other isocyanate-reactive substances, such as those described in moredetail below as well as other isocyanate-reactive substances known orconventionally used in two component laminating adhesives, may also bepresent in Component B, if so desired.

Isocyanate-reactive substances generally include those compounds whichare active hydrogen-functionalized. “Active hydrogen-functionalized” asused herein refers to a functional group containing a hydrogen atomwhich, because of its position in the compound, displays significantactivity according to the Zerewitnoff test described by Wohler in theJournal of the American Chemical Society, Vol. 49, p. 3181 (1927).Suitable isocyanate-reactive substances include those polymericsubstances having about 2 to about 4 functional groups containing activehydrogen which are capable of reacting with isocyanate such as hydroxyland primary or secondary amino groups. The isocyanate-reactive substancemay have a number average molecular weight of from about 200 to about100,000. In another embodiment, the molecular weight is from about 500to about 50,000. Polyester polyols, polyether polyols, polyether esterpolyols and mixtures thereof may be utilized. Examples of polyesterpolyols are those obtained by reacting dibasic acids such asterephthalic acid, isophthalic acid, adipic acid, azaelaic acid andsebacic acid, dialkyl esters thereof and mixtures thereof with glycolssuch as ethylene glycol, propylene glycol, diethylene glycol, butyleneglycol, neopentyl glycol, 2-methyl-1, 3-propanediol, 1,6-hexanediol andmixtures thereof.

Polycaprolactone polyols may also be used. Exemplary polyether polyolsinclude those obtained by polymerizing oxirane compounds such asethylene oxide, propylene oxide, butylene oxide, oxirane andtetrahydrofuran using water or low molecular weight polyols such asethylene glycol, propylene glycol, trimethylol propane or glycerin as aninitiator. Copolymers of oxiranes (including random, block, andend-capped copolymers) are also suitable for use.

Examples of polyether ester polyols include those obtained by reactingpolyether polyols with dibasic acids such as those mentioned hereinabove in connection with polyester polyols.

Low molecular weight polyhydroxy compounds having a number averagemolecular weight of less than 200 may also be used in Component Bconjointly with the primary hydroxyl-containing curative prepared by themultistage process previously described herein. Suitable polyhydroxycompounds of this type include ethylene glycol, propylene glycol,butylene glycol, diethylene glycol, dipropylene glycol, hexylene glycol,neopentyl glycol, cyclohexene dimethanol, glycerin andtrimethylolpropane.

Specific mention may be made of the following isocyanate-reactivesubstances suitable for use in Component B in addition to the curativeproduced by the multistage process described herein:

-   -   saturated and unsaturated glycols such as ethylene glycol or        condensates of ethylene glycol, butane-1,3-diol,        butane-1,4-diol, 2-butene-1,4-diol, 2-butyne-1,4-diol,        propane-1,2-diol, propane-1,3-diol, neopentyl glycol,        hexanediol, bishydroxymethylcyclohexane,        dioxyethoxyhydroquinone, bis-glycol terephthalate,        N,N′-di(2-hydroxyethyl)succinamide,        N,N′-dimethyl-N,N′-di(2-hydroxy-ethyl)succinamide,        1,4-di(2-hydroxymethyl-mercapto)-2,3,5,6-tetrachlorobenzene,        2-methylene-propane-1,3-diol, 2-methylpropane-1,3-diol,        3-pyrrolidino-1,2-propanediol, 2-methylenepentane-2,4-diol,        3-alkoxy-1,2-propanediol, 2-ethylhexane-1,3-diol,        2,2-dimethylpropane-1,3-diol, 1,5-pentanediol,        2,5-dimethyl-2,5-hexanediol, 3-phenoxy-1,2-propanediol,        3-benzyloxy-1,2-propanediol, 2,3-dimethyl-2,3-butanediol,        3-(4-methoxyphenoxy)-1,2-propanediol, and hydroxymethylbenzyl        alcohol;    -   aliphatic, cycloaliphatic, and aromatic diamines such as        ethylenediamine, hexamethylenediamine, 1,4-cyclohexylenediamine,        piperazine, N-methylpropylenediamine, diaminodiphenyl sulfone,        diaminodiphenyl ether, diaminodiphenyldimethyl-methane,        2,4-diamino-6-phenyltriazine, isophoronediamine, dimer fatty        acid diamine, diaminodiphenylmethane, aminodiphenylamine or the        isomers of phenylenediamine;    -   carbohydrazides or hydrazides of dicarboxylic acids;    -   amino alcohols such as ethanolamine, propanolamine,        butanolamine, N-methylethanolamine, N-methylisopropanolamine,        diethanolamine, triethanolamine, and higher di- or        tri(alkanolamines);    -   aliphatic, cycloaliphatic, aromatic and heterocyclic mono- and        diaminocarboxylic acids such as glycine, 1- and 2-alanine,        6-aminocaproic acid, 4-aminobutyric acid, the isomeric mono- and        diaminobenzoic acids, and the isomeric mono- and        diaminonaphthoic acids.

Component B may also comprise a hydroxy-functional natural oil or fatsuch as, for example, castor oil, and/or an epoxidized natural oil orfat which has been ring-opened with one or more alcohols.

Component A of the present invention contains at least one compoundhaving two or more isocyanate groups per molecule. The isocyanate groupsmay be free —NCO groups, but can also be blocked or masked —NCO groups.One particular embodiment of the invention employs one or moreisocyanate-functionalized polyurethane prepolymers in Component A. Inthe context of the present invention, a polyurethane prepolymer is acompound such as results, for example, from the reaction of a polyolcomponent with at least one isocyanate having a functionality of atleast two. This reaction can take place without solvent or in a solvent,ethyl acetate, acetone or methyl ethyl ketone, for example. The term“polyurethane prepolymer” embraces not only compounds having arelatively low molecular weight, such as are formed, for example, fromthe reaction of a polyol with an excess of polyisocyanate, but alsooligomeric or polymeric compounds. “Perfect” polyurethane prepolymers,containing a single polyol moiety capped at each end or terminus with apolyisocyanate moiety and very little, if any, free polyisocyanatemonomer or oligomeric or polymeric compounds (containing two or morepolyol moieties per molecule) may also be utilized.

Molecular weight figures based on polymeric compounds refer, unlessotherwise indicated, to the numerical average of the molecular weight(M_(n)). The polyurethane prepolymers used in the context of the presentinvention generally may have a molecular weight of from 500 to 27,000,alternatively from 700 to 15,000, or alternatively from 700 to 8,000g/mol.

Likewise embraced by the term “polyurethane prepolymers” are compoundsas formed, for example, from the reaction of a trivalent or tetravalentpolyol with a molar excess of diisocyanates, based on the polyol. Inthis case one molecule of the resultant compound bears two or moreisocyanate groups.

Polyurethane prepolymers having isocyanate end groups are well known inthe art. They can be crosslinked or chain-extended with suitable curingagents—usually polyfunctional alcohols—in a simple way to formsubstances of higher molecular weight. To obtain polyurethaneprepolymers having terminal isocyanate groups it is customary to reactpolyfunctional alcohols with an excess of polyisocyanates, generally atleast predominantly diisocyanates. In this case the molecular weight canbe controlled at least approximately by way of the ratio of OH groups toisocyanate groups. While a ratio of OH groups to isocyanate groups of1:1 or near to 1:1 often leads to substances with high molecularweights, it is the case with a ratio of approximately 2:1, for example,when using diisocyanates, that one diisocyanate molecule is attached onaverage to each OH group, so that in the course of the reaction, in theideal case, there is no oligomerization or chain extension.

Excess unreacted polyisocyanate monomer may be removed from thepolyurethane prepolymer reaction product initially obtained by any knownmethod such as, for example, distillation to provide a prepolymer havinga desirably low level of polyisocyanate monomer (e.g., less than 1weight %).

Polyurethane prepolymers are customarily prepared by reacting at leastone polyisocyanate, preferably a diisocyanate, and at least onecomponent having functional groups which are reactive toward isocyanategroups, generally a polyol component, which is preferably composed ofdiols. The polyol component may contain only one polyol, although it isalso possible to use a mixture of two or more polyols as the polyolcomponent. By a polyol is meant a polyfunctional alcohol, i.e., acompound having more than one OH group in the molecule. By “functionalgroups which are reactive toward isocyanate groups” are meant, in thecontext of the present text, functional groups which can react withisocyanate groups to form at least one covalent bond.

Suitable reactive functional groups containing active hydrogen may bemonofunctional in the sense of a reaction with isocyanates: OH groups ormercapto groups, for example. Alternatively, they may also bedifunctional with respect to isocyanates: amino groups, for example. Amolecule containing a primary amino group, accordingly, also has twofunctional groups which are reactive toward isocyanate groups. In thiscontext it is unnecessary for a single molecule to have two separatefunctional groups that are reactive toward isocyanate groups. What iscritical is that the molecule is able to connect with two isocyanategroups with the formation in each case of one covalent bond.

As the polyol component it is possible to use a multiplicity of polyols.These are, for example, aliphatic alcohols having from 2 to 4 OH groupsper molecule. The OH groups may be both primary and secondary. Examplesof suitable aliphatic alcohols include ethylene glycol, propyleneglycol, butane-1,4-diol, pentane-1,5-diol, hexane-1,6-diol,heptane-1,7-diol, octane-1,8-diol and their higher homologs or isomerssuch as result in a formal sense from a stepwise extension of thehydrocarbon chain by one CH₂ group in each case or with the introductionof branches into the carbon chain. Likewise suitable are higherpolyfunctional alcohols such as, for example, glycerol,trimethylolpropane, pentaerythritol and also oligomeric ethers of saidsubstances with themselves or in a mixture of two or more of said etherswith one another.

As the polyol component it is additionally possible to use reactionproducts of low molecular weight polyfunctional alcohols with alkyleneoxides, referred to as polyether polyols. The alkylene oxides havepreferably 2 to 4 carbon atoms. Suitable examples are the reactionproducts of ethylene glycol, propylene glycol, the isomeric butanediols,hexanediols or 4,4′-dihydroxy-diphenylpropane with ethylene oxide,propylene oxide or butylene oxide, or with mixtures of two or morethereof. Also suitable, furthermore, are the reaction products ofpolyfunctional alcohols, such as glycerol, trimethylolethane ortrimethylolpropane, pentaerythritol or sugar alcohols, or mixtures oftwo or more thereof, with the stated alkylene oxides to form polyetherpolyols. Particularly suitable polyether polyols are those having amolecular weight from about 100 to about 10,000, preferably from about200 to about 5,000. Likewise suitable as the polyol component arepolyether polyols such as are formed, for example, from thepolymerization of tetrahydrofuran.

The polyethers may be synthesized using methods known to the skilledworker, by reaction of the starting compound having a reactive hydrogenatom with alkylene oxides: for example, ethylene oxide, propylene oxide,butylene oxide, styrene oxide, tetrahydrofuran or epichlorohydrin ormixtures of two or more thereof. Examples of suitable starting compoundsare water, ethylene glycol, propylene 1,2-glycol or 1,3-glycol, butylene1,4-glycol or 1,3-glycol, hexane-1,6-diol, octane-1,8-diol,neopentylglycol, 1,4-hydroxymethylcyclohexane, 2-methyl-1,3-propanediol,glycerol, trimethylolpropane, hexane-1,2,6-triol, butane-1,2,4-triol,trimethylolethane, pentaerythritol, mannitol, sorbitol,methylglycosides, sugars, phenol, isononylphenol, resorcinol,hydroquinone, 1,2,2- or 1,1,2-tris(hydroxyphenyl)ethane, ammonia,methylamine, ethylenediamine, tetra- or hexamethyleneamine,triethanolamine, aniline, phenylenediamine, 2,4- and 2,6-diaminotolueneand polyphenylpolymethylene-polyamines, such as are obtainable byaniline-formaldehyde condensation, or mixtures of two or more thereof.

Likewise suitable for use as the polyol component are polyethers whichhave been modified by vinyl polymers. Products of this kind areavailable, for example, by polymerizing styrene or acrylonitrile, or amixture thereof, in the presence of polyethers.

Polyester polyols having a molecular weight of from about 200 to about10,000 are likewise suitable as the polyol component. Thus, for example,it is possible to use polyester polyols formed by reacting low molecularweight alcohols, especially ethylene glycol, diethylene glycol,neopentyl glycol, hexanediol, butanediol, propylene glycol, glycerol ortrimethylolpropane, with caprolactone. Likewise suitable aspolyfunctional alcohols for preparing polyester polyols are1,4-hydroxymethylcyclohexane, 2-methyl-1,3-propanediol,butane-1,2,4-triol, triethylene glycol, tetraethylene glycol,polyethylene glycol, dipropylene glycol, polypropylene glycol,dibutylene glycol and polybutylene glycol.

Further suitable polyester polyols are preparable by polycondensation.For instance, difunctional and/or trifunctional alcohols can becondensed with a substoichiometric amount of dicarboxylic acids and/ortricarboxylic acids, or their reactive derivatives (e.g., anhydrides,esters), to form polyester polyols. Examples of suitable dicarboxylicacids are adipic acid or succinic acid and their higher homologs havingup to 16 carbon atoms, unsaturated dicarboxylic acids such as maleicacid or fumaric acid, and also aromatic dicarboxylic acids, particularlythe isomeric phthalic acids, such as phthalic acid, isophthalic acid orterephthalic acid. Examples of suitable tricarboxylic acids are citricacid or trimellitic acid. These acids may be used individually or asmixtures of two or more thereof. Particularly suitable alcohols arehexanediol, ethylene glycol, 1,4-butanediol, diethylene glycol, glycerolor neopentyl glycol or mixtures of two or more thereof. Typically, theconditions used in such polycondensation reactions to form thepolyhydroxyl-functionalized polyester will be similar to thosepreviously described in connection with the reaction of polyols withpolybasic acids, polybasic acid esters or polybasic acid anhydrides toform the intermediate used in the preparation of the curatives of thepresent invention. To obtain hydroxyl end groups, an excess of hydroxylequivalents relative to carboxyl equivalents is employed. Typically,hydroxyl:carboxyl equivalent ratios range from about 2:1 to about 15:14.The nearer this ratio is to unity, the higher the molecular weight ofthe polyhydroxyl-functionalized polyester will be. The extent ofconversion of carboxylic acid groups (or equivalents thereof) to estergroups (as part of the polyester formed) is typically at least 99%, morepreferably at least about 99.9%. Particularly suitable acids includeisophthalic acid, orthophthalic acid anhydride and adipic acid and theirmixtures. Particularly suitable di- and trifunctional alcohols which canbe used in combination with the hydroxyl-functionalizedtransesterification product include ethylene glycol, ethylene glycololigomers (e.g., diethylene glycol), polypropylene glycol, glycerin andmixtures thereof.

Polyester polyols of high molecular weight include, for example, thereaction products of polyfunctional alcohols, preferably difunctionalalcohols (together where appropriate with small amounts of trifunctionalalcohols) and polyfunctional carboxylic acids, preferably difunctionalcarboxylic acids. Instead of free polycarboxylic acids use may also bemade (if possible) of the corresponding polycarboxylic anhydrides orcorresponding polycarboxylic esters with alcohols having preferably 1 to3 carbon atoms. The polycarboxylic acids may be aliphatic,cycloaliphatic, aromatic or heterocyclic or both. They may whereappropriate be substituted, by alkyl groups, alkenyl groups, ethergroups or halogens, for example. Examples of suitable polycarboxylicacids include succinic acid, adipic acid, suberic acid, azelaic acid,sebacic acid, phthalic acid, isophthalic acid, terephthalic acid,trimellitic acid, phthalic anhydride, tetrahydrophthalic anhydride,hexahydrophthalic anhydride, tetra-chlorophthalic anhydride,endomethylenetetrahydrophthalic anhydride, glutaric anhydride, maleicacid, maleic anhydride, fumaric acid, dimer fatty acid or trimer fattyacid or mixtures of two or more thereof. Where appropriate, minoramounts of monofunctional fatty acids may be present in the reactionmixture.

The polyesters may where appropriate contain a small fraction ofcarboxyl end groups. Polyesters obtainable from lactones, ε-caprolactonefor example, or hydroxy-carboxylic acids, ω-hydroxycaproic acid forexample, may likewise be used.

Polyacetals and polyester ether polyols are likewise suitable as thepolyol component. By polyacetals are meant compounds obtainable fromglycols reacted with aldehydes, for example, diethylene glycol orhexanediol or a mixture thereof condensed with formaldehyde. Polyacetalswhich can be used in the context of the invention may likewise beobtained by the polymerization of cyclic acetals.

Further suitable polyols include polycarbonates. Polycarbonates can beobtained, for example, by reacting diols, such as propylene glycol,butane-1,4-diol or hexan-1,6-diol, diethylene glycol, triethylene glycolor tetraethylene glycol, or mixtures of two or more thereof, with diarylcarbonates, for example, diphenyl carbonate, or phosgene.

Likewise suitable as the polyol component are polyacrylates which carryOH groups. These polyacrylates are obtainable, for example, bypolymerizing ethylenically unsaturated monomers which carry an OH group.Monomers of this kind are obtainable, for example, by esterifyingethylenically unsaturated carboxylic acids and difunctional alcohols,the alcohol generally being present in a slight excess. Examples ofethylenically unsaturated carboxylic acids suitable for this purpose areacrylic acid, methacrylic acid, crotonic acid or maleic acid.Corresponding esters carrying OH groups are, for example, 2-hydroxyethylacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate,2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropylacrylate or 3-hydroxypropylmethacrylate or mixtures of two or morethereof.

In addition to the aforedescribed polyol compounds, polyisocyanates areimportant building blocks of the polyurethane prepolymers which can beused in Component A of the two component laminating adhesives of thepresent invention. These include all of the polyisocyanates mentioned ordescribed previously in connection with the preparation of the curativesof the present invention.

The amounts of Component A and Component B used in the laminatingadhesive systems of this invention will generally be adjusted so as toprovide an NCO/active hydrogen equivalent ratio in the range of fromabout 1 to 10 in one embodiment of the invention, from about 1.05 toabout 5 in another embodiment, and from about 1.1 to about 2 in yetanother embodiment. Typically, the free isocyanate content (prior to anyreaction between Component A and Component B) will be from about 1% toabout 25% by weight based on the total weight of the two componentadhesive.

Where appropriate, in addition to the isocyanate-functionalizedcompound(s) and active hydrogen-functionalized compound(s) previouslydescribed, the two component laminating adhesive of the invention maycomprise one or more further additives. The additives may, for example,account for up to about 10% by weight of the overall two componentadhesive.

The optional additives which can be used in the context of the presentinvention include solvents (although preferably the two componentlaminating adhesive is essentially free of solvent), water, adhesionpromoters, catalysts, plasticizers, stabilizers, antioxidants, lightstabilizers, fillers, dyes, pigments, fragrances, preservatives ormixtures thereof.

The film or films to be coated or adhered to each other using the twocomponent formulations of the present invention may be comprised of anyof the materials known in the art to be suitable for use in flexiblepackaging, including both polymeric and metallic materials as well aspaper (including treated or coated paper). Thermoplastics areparticularly preferred for use as at least one of the layers. Thematerials chosen for individual layers in a laminate are selected toachieve specific desired combinations of properties, e.g., mechanicalstrength, tear resistance, elongation, puncture resistance,flexibility/stiffness, gas and water vapor permeability, oil and greasepermeability, heat sealability, adhesiveness, optical properties (e.g.,clear, translucent, opaque), formability, merchantability and relativecost. Individual layers may be pure polymers or blends of differentpolymers. The polymeric layers are often formulated with colorants,anti-slip, anti-block, and anti-static processing aids, plasticizers,lubricants, fillers, stabilizers and the like to enhance certain layercharacteristics.

Particularly preferred polymers for use in the present inventioninclude, but not limited to, polyethylene (including low densitypolyethylene (LDPE), medium density polyethylene (MDPE), high densitypolyethylene (HPDE), high molecular weight, high density polyethylene(HMW-HDPE), linear low density polyethylene (LLDPE), linear mediumdensity polyethylene (LMPE)), polypropylene (PP), orientedpolypropylene, polyesters such as poly (ethylene terephthalate) (PET)and poly (butylene terephthalate) (PBT), ethylene-vinyl acetatecopolymers (EVA), ethylene-acrylic acid copolymers (EAA),ethylene-methyl methacrylate copolymers (EMA), ethylene-methacrylic acidsalts (ionomers), hydrolyzed ethylene-vinyl acetate copolymers (EVOH),polyamides (nylon), polyvinyl chloride (PVC), poly(vinylidene chloride)copolymers (PVDC), polybutylene, ethylene-propylene copolymers,polycarbonates (PC), polystyrene (PS), styrene copolymers, high impactpolystyrene (HIPS), acrylonitrile-butadiene-styrene polymers (ABS), andacrylonitrile copolymers (AN).

The polymer surface may be treated or coated, if so desired. Forexample, a film of polymer may be metallized by depositing a thin metalvapor such as aluminum onto the film's surface. Metallization mayenhance the barrier properties of the finished laminate. A coating of aninorganic oxide such as silicon dioxide or aluminum oxide may also bepresent on the surface of the polymeric film. The polymer film surfacemay also be coated with anti-fog additive or the like or subjected to apretreatment with electrical or corona discharges, or ozone or otherchemical agents to increase its adhesive receptivity.

One or more layers of the laminate may also comprise a metal foil, suchas aluminum foil, or the like. The metal foil will preferably have athickness of about 5 to 100 μm.

The individual films comprising the laminates of the present inventioncan be prepared in widely varying thicknesses, for example, from about 5to about 200 microns. The films, foils, and laminating adhesiveformulation can be assembled into the laminate by using any one or moreof the several conventional procedures known in the art for suchpurpose. For instance, the adhesive formulation may be applied to thesurface of one or both of two films/foils by means of extrusion,brushes, rollers, blades, spraying or the like and the film/foilsurfaces bearing the adhesive composition brought together and passedthrough a set of rollers (often referred to as nip rollers) which presstogether the film/foils having the adhesive composition between thefilms/foils. The resulting laminate may be rolled or wound onto a reel.The adhesive obtained by combining Components A and B may be applied byconventional techniques; e.g., by a multi-roll application station.

Typically, the rate at which the adhesive formulation is applied to thesurface of a film or foil is in the range of about 0.2 to about 5 g/m².For example, the two components of the adhesive formulation may bepumped from separate drums or tanks at from about room temperature toabout 40° C., mixed in the desired ratio using standard methods andequipment (for example, a meter-mix unit) and applied using solventlessapplication machinery having the capability of being heated from about25° C. to about 90° C. The adhesive composition of the present inventionis utilized as a two component system wherein the two components arecombined shortly before use. It may be desirable to heat the laminate atan elevated temperature (e.g., about 40° C. to about 100° C.) so as toaccelerate full curing of the adhesive composition. Alternatively, theadhesive composition may be adjusted so as to be curable atapproximately room temperature (e.g., about 20° C. to about 40° C.) overa period of from about 1 hour to about 7 days. Radiation may also beused to increase the cure rate of the adhesive.

Generally speaking, the adhesive compositions of the present inventionare believed to be largely chemically cured through the reaction of theformulation constituents containing isocyanate groups and theconstituents containing hydroxyl or other active hydrogen groups (e.g.,the curative obtained by way of the multistage process previouslydescribed). However, curing can also be accomplished at least in partthrough moisture curing. Although sufficient moisture may be inherentlypresent on the film or foil surfaces for this purpose, water may also bedeliberately introduced through conventional methods if so desired.

Laminates prepared in accordance with the present invention may be usedfor packaging purposes in the same manner as conventional or knownflexible laminated packaging films. The laminates are particularlysuitable for forming into flexible pouch-shaped container vesselscapable of being filed with a foodstuff and retorted. For example, tworectangular or square sheets of the laminate may be piled in the desiredconfiguration or arrangement; preferably, the two layers of the twosheets which face each other are capable of being heat-sealed to eachother. Three peripheral portions of the piled assembly are thenheat-sealed to form the pouch. Heat-sealing can easily be accomplishedby means of a heating bar, heating knife, heating wire, impulse sealer,ultrasonic sealer, or induction heating sealer.

The foodstuff is thereafter packed in the so-formed pouch. If necessary,gasses injurious to the foodstuff such as air are removed by known meanssuch as vacuum degasification, hot packing, boiling degasification, orsteam jetting or vessel deformation. The pouch opening is then sealedusing heat. The packed pouch may be charged to a retorting apparatus andsterilized by heating to a temperature greater than about 100° C.

EXAMPLES Example 1 (Comparative)

Glycerol (5.5 equivalents, based on hydroxyl; 31% by weight of totalreaction mixture) and polypropylene glycol (1025 number averagemolecular weight; 0.5 equivalents, based on hydroxyl; 47% by weight oftotal reaction mixture) were combined and reacted with adipic acid (2equivalents, based on carboxyl; 27% by weight of total reaction mixture)at 227 degrees C. under vacuum. After esterification, the reactionproduct separated due to poor reaction of the secondary hydroxyl groupsof the polypropylene glycol.

Example 2

Polypropylene glycol (1025 number average molecular weight; 2equivalents, based on hydroxyl; 72% by wt of total reaction mixture) wasreacted alone with adipic acid (4 equivalents, based on carboxyl; 27% bywt of total reaction mixture) at 238 degrees C. to an acid number of 99to carboxyl end-cap the first stage and react the secondary hydroxylgroups of the polypropylene glycol. The reaction mixture was cooled to160 degrees C. and glycerol (6 equivalents, based on hydroxyl; 13% by wtof total reaction mixture) was then added. The second stage wasesterified at 230 degrees C. until the acid number was less than 3.0.The reaction product was then dried by vacuum for an hour at 26 inchesmercury at 231 degrees C. The curative obtained had an equivalent weight(based on hydroxyl) of 355 and a viscosity of 4300 cps at 25 degrees C.and was stable and did not separate. When 1 part by weight of thecurative was reacted with 1.35 parts by weight of anisocyanate-functionalized polyurethane prepolymer (16 weight % NCO), atough clear adhesive resulted.

Example 3

Polypropylene glycol (2025 number average molecular weight; 2equivalents, based on hydroxyl; 72% by wt of total reaction mixture) wasreacted alone with adipic acid (4 equivalents, based on carboxyl; 27% byweight of total reaction mixture) at 239 degrees C. for 2 hours tocarboxyl end-cap the first stage and react the secondary hydroxyl groupsof the polypropylene glycol. The reaction mixture was cooled andglycerol (6 equivalents, based on hydroxyl; 13% by weight of totalreaction mixture) was then added. The second stage was esterified at 230degrees C. until the acid number was less than 3.0. The reaction mixturewas then dried under vacuum for an hour at 26 inches mercury and 231degrees C. The curative obtained had a hydroxyl equivalent weight of 611and a viscosity of 2700 cps at 25 degrees C. and was stable and did notseparate. When 1 part by weight of the curative was reacted with 1.16parts by weight of an isocyanate-functionalized prepolymer (16 weight %NCO), a tough clear adhesive resulted.

Example 4

Polypropylene glycol (425 number average molecular weight; 1.66equivalents, based on hydroxyl; 72% by weight of total reaction mixture)was reacted alone with adipic acid (10 equivalents, based on carboxyl;27% by weight of total reaction mixture) at 230 degrees C. for 2 hoursto carboxyl end-cap the first stage and react the secondary hydroxylgroups of the polypropylene glycol. The reaction mixture was cooled to160 degrees C. and glycerol (6 equivalents, based on hydroxyl; 13% byweight of total reaction mixture) and diethylene glycol (5.58equivalents, based on hydroxyl) were then added. The second stage wasesterified using a packed column (to contain the diethylene glycol) at230 degrees C. until the acid number was less than 10.0. The reactionmixture was then dried under vacuum for an hour at 26 inches mercury and229 degrees C. The curative obtained had a hydroxyl equivalent weight of579 and a viscosity of 4500 cps at 25 degrees C. and was stable and didnot separate. When 150 parts by weight of the curative was reacted with100 parts by wt of an isocyanate-functionalized polyurethane prepolymer(16 weight % NCO), a tough adhesive resulted.

Example 5

Polypropylene glycol (1025 number average molecular weight; 2equivalents, based on hydroxyl; 67.9% by weight of total reactionmixture) was reacted alone with orthophthalic anhydride (4 equivalents,based on carboxyl; 19.0% by weight of total reaction mixture) at 153degrees C. for 2 hours to carboxyl end-cap the first stage (forming thehalf ester of orthophthalic anhydride) and react the secondary hydroxylgroups of the polypropylene glycol. The reaction mixture was cooled to134 degrees C. and diethylene glycol (4 equivalents, based on hydroxyl,15.1% of total reaction mix) was then added. The second stage wasesterified using a packed column (to contain the diethylene glycol) at230 degrees C. until the acid number was less than 3.0. The reactionmixture was then dried under vacuum for a half hour at 26 inches mercuryand 239 degrees C. The curative obtained had a hydroxyl equivalentweight of 760, a viscosity of 4500 cps at 25 degrees C. and was stableand did not separate. When 200 parts by weight of the curative wasreacted with 100 parts by weight of an isocyanate-functionalizedpolyurethane prepolymer (16 weight % NCO), a flexible adhesive resulted.

1. A two component laminating adhesive comprising Component A and Component B, wherein Component A comprises at least one isocyanate-functionalized compound and Component B comprises a curative containing at least about two primary hydroxyl groups per molecule, said curative having been obtained by a process comprising reacting a first polyol containing predominately secondary hydroxyl groups with a stoichiometric excess of a reactant selected from the group consisting of polybasic acids, polybasic acid anhydrides, polybasic acid esters, and polyisocyanates to form an intermediate containing at least about two terminal functional groups per molecule selected from the group consisting of isocyanate, carboxylic acid and carboxylic acid ester and reacting said intermediate with a stoichiometric excess of a second polyol containing predominately primary hydroxyl groups.
 2. The two component laminating adhesive of claim 1 wherein said first polyol is a polyalkylene glycol containing secondary hydroxyl groups.
 3. The two component laminating adhesive of claim 1 wherein said first polyol is a polypropylene glycol.
 4. The two component laminating adhesive of claim 1, wherein Component A comprises an isocyanate-functionalized polyurethane prepolymer.
 5. The two component laminating adhesive of claim 1, wherein said reactant is selected from the group consisting of aliphatic linear saturated dicarboxylic acids containing from 4 to 12 carbon atoms, phthalic acids, orthophthalic acid anhydride, and mixtures thereof.
 6. The two component laminating adhesive of claim 1, wherein said second polyol is an aliphatic compound containing 2 to 5 hydroxyl groups per molecule and the ratio of primary hydroxyl groups to secondary hydroxyl groups in the second polyol is at least 2:1.
 7. The two component laminating adhesive of claim 1, wherein said second polyol is selected from the group consisting of ethylene glycol, ethylene glycol oligomers, 1,4-butanediol, 1,6-hexanediol, glycerol, trimethylolpropane, trimethylolethane, 1,2,6-hexanetriol, 1,2,4-butanetriol, and mixtures thereof.
 8. The two component laminating adhesive of claim 1, wherein said curative contains an average of about two to about four hydroxyl groups per molecule.
 9. The two component laminating adhesive of claim 1, wherein said reactant is selected from the group consisting of adipic acid, orthophthalic acid anhydride, and mixtures thereof.
 10. (canceled)
 11. (canceled)
 12. (canceled)
 13. (canceled)
 14. (canceled)
 15. (canceled)
 16. (canceled)
 17. (canceled)
 18. (canceled)
 19. (canceled)
 20. (canceled)
 21. A method of making a curative comprising: providing a first polyol containing predominately secondary hydroxyl groups; providing a reactant selected from the group consisting of polybasic acids, polybasic acid anhydrides, polybasic acid esters, and polyisocyanates; reacting the first polyol containing predominately secondary hydroxyl groups with a stoichiometric excess of the reactant selected from the group consisting of polybasic acids, polybasic acid anhydrides, polybasic acid esters, and polyisocyanates to form an intermediate containing at least about two terminal functional groups per molecule selected from the group consisting of isocyanate, carboxylic acid and carboxylic acid ester; providing a second polyol containing predominately primary hydroxyl groups; adding a stoichiometric excess of the second polyol containing predominately primary hydroxyl groups to the already formed intermediate; and reacting the intermediate with the stoichiometric excess of the second polyol containing predominately primary hydroxyl groups to form the curative, the curative having at least about two primary hydroxyl groups per molecule; wherein the curative will not separate and will react with an isocyanate-functionalized compound to provide a curable laminating adhesive.
 22. The method of claim 21 wherein the reactant is reacted with the first polyol at a molar ratio of at least about 2:1.
 23. The method of claim 21 wherein the intermediate is reacted with the second polyol for a time and at a temperature effective to convert essentially all of the terminal functional groups on the intermediate to either urethane or ester groups.
 24. The method of claim 21 wherein the curative has the structure: Y—O—C(═O)—Z—C(═O)—O—CH(CH₃)—CH₂—O—(C₃H₆O)_(n)—CH₂—CH(CH₃)—O—C(═O)—Z′—C(═O)—O—Y′ wherein Y and Y′ are the same or different and are selected from the group consisting of HO—CH₂—CH(OH)—CH₂— and HO—(CH₂—CH₂—O—)_(p)—CH₂—CH₂—; Z and Z′ are the same or different and are selected from the group consisting of —C₆H₄—, —(CH₂)_(o)— and combinations thereof; p is 0 or an integer of 1 to 3; m and o are the same or different and are integers of from 2 to 10; and n is 0 or an integer of from 1 to
 100. 25. The method of claim 24 wherein n is an integer of from 4 to
 50. 26. A laminating adhesive including: Component A comprising an isocyanate-functionalized compound; and Component B comprising the curative of claim
 21. 27. The laminating adhesive of claim 26, including: Component A comprising a compound having two or more isocyanate groups per molecule; and Component B comprising the curative of claim 21 and a hydroxy-functional natural oil or fat.
 28. The laminating adhesive of claim 26, including: Component A comprising a compound having two or more isocyanate groups per molecule; and Component B comprising 1% to 100% by weight of the curative of claim
 21. 29. The laminating adhesive of claim 26, including: Component A comprising a compound having two or more isocyanate groups per molecule; and Component B comprising 1% to 100% by weight of the curative of claim
 21. 30. The laminating adhesive of claim 26, including: Component A comprising a compound having two or more isocyanate groups per molecule; and Component B comprising 40% to 70% by weight of the curative of claim
 21. 31. A flexible film laminate comprising: (a) a first layer comprised of a first polyolefin film or first polyester film; (b) a second layer comprised of a second polyolefin film, which may be the same or different from the first polyolefin film, a second polyester film, which may be the same as or different from the first polyester film, or a metal foil; (c) an adhesive layer bonding the first layer to the second layer, said adhesive layer being a mixture of Component A comprising a compound having two or more isocyanate groups per molecule and Component B comprising 1% to 100% by weight of the curative of claim
 21. 